This invention relates to terrain estimation useful in the provision of a map of altitude of the earth's surface versus position along the earth's surface and, more particularly, to the formation of a terrain estimate based on a succession of measurements of the gravity gradient by a gradiometer, the measurements being conducted in conjunction with inertial navigation which locates the gradiometer.
Various techniques for mapping the earth's terrain are presently available, such as the use of side-looking radar, radar-height finding, and photography at visible and infrared regions of the spectrum, by way of example. Such techniques are dependent on the reception of radiant energy from the terrain being mapped. In the case of the radar mapping, the process includes the transmission of a radar beam to illuminate the terrain being mapped.
A problem arises in that the foregoing techniques are disadvantageous in that only certain features can be mapped, as distinguished from anomalies such as oil fields or iron deposits located beneath the earth's surface. Also, the foregoing techniques may require the transmission of radiation, a disadvantage if covert operation is preferred, as well as the reception of radiation, a disadvantage in the presence of adverse atmospheric conditions.